1. Field of the Invention
The present invention relates to an adsorbent molded article intended primarily for use in electronic or optical equipment housings; to an adsorbent unit employing said molded article; and to a housing employed by said adsorbent molded article or adsorbent unit.
2. Description of Related Art
It is known that in electronic or optical equipment, such as hard disk drive units, equipment service life is significantly affected by the presence of moisture or other gases within the unit.
For example, in organic electroluminescent (EL) displays, which have drawn considerable attention in recent years as the “next generation” of displays, the light emission characteristics of the organic EL elements (i.e. luminance, uniformity of light emission, etc.) clearly degrade over time due to the effects of even trace amounts of moisture.
Adsorbents for placement in the housing of housing-enclosed piece of optical or electronic equipment, such as an organic EL element, for the purpose of adsorbing moisture or other gases having adverse effects on the equipment, must be able to sustain moisture absorbing ability over an indefinite period.
Where the housing of a piece of optical or electronic equipment is a semi-hermetic enclosure, it is common practice to seal the cover and enclosure body together with a sealing resin (bonding adhesive) or by means of screws with a gasket interposed; eventually, moisture outside the housing will gradually infiltrate through the sealing resin or gasket portion, causing the optical or other equipment to degrade over time. Accordingly, the bonding adhesive must adsorb and remove not only moisture trapped in the housing during fabrication of the optical equipment, but also moisture gradually infiltrating during service.
Degradation of organic EL elements over time is known to occur through the following mechanism. Moisture adsorbed onto surfaces of components of organic EL elements or penetrating into organic EL elements eventually penetrates into structures composed of a pair of electrodes and a luminescent material sandwiched between the electrodes (hereinbelow sometimes referred to as “organic EL structures”), penetrating into gaps or other flaws on the cathode surface, resulting in delamination of the luminescent material and cathode. Since current flow is hindered through the delaminated area, the area appears as a defective pixel (“dark spot”).
To avoid the problem of deterioration in organic EL elements over time, there have been proposed a number of methods for housing organic EL elements within a hermetic enclosure, and additionally arranging an adsorbent within the enclosure, in order to adsorb out moisture in the enclosure as well as any other gases that could degrade the organic EL elements.
Kokai 3-261091, for example, teaches an organic EL element wherein the organic EL structures are housed within an airtight case, with desiccant means containing diphosphorus pentaoxide arranged therein, isolated from the organic EL structures. However, as this technique entails deliquescence of the diphosphorus pentaoxide through adsorption of moisture within the airtight case, it is difficult to keep the desiccant means isolated from the organic EL structures within the case. In the event that the deliquesced diphosphorus pentaoxide should leak from the airtight case, the organic EL structures could become contaminated and possible malfunction. It is therefore necessary to contain deliquesced diphosphorus pentaoxide within the case in such a way that it does not leak, and the higher production cost entailed in achieving this may make such devices impractical.
Kokai 9-148066 teaches an organic EL element that, instead of desiccant means containing diphosphorus pentaoxide, employs desiccant means comprising a compound that chemical adsorbs water, as well as remaining solid as it adsorbs moisture (i.e., a so-called chemical adsorbent).
Kokai 2001-278999 teaches a gaseous component treatment sheet material composed of gas-permeable matrix film having dispersed therein a remover of particulate form that removes specific gaseous components, and an EL element comprising said sheet material. Moisture is also targeted as a component for removal, and several kinds of desiccants can be cited as examples of the remover. Kokai 2002-43055 teaches an organic EL element that, instead of desiccant means of Kokai 3-261091, employs a hygroscopic molded article composed of hygroscopic material and a resin component. These techniques employ particulate hygroscopic material in the form of a molded article (sheet), which offers the advantages of ease of handling during organic EL element fabrication, and low cost.
However, the adsorbents (hygroscopic materials) used in the techniques taught in Kokai 9-148066, Kokai 2001-278999 and Kokai 2002-43055 experience a sharp drop in the rate of moisture adsorption subsequent to fabrication of the organic EL element, after adsorbing moisture at a relatively early stage, as a result of which moisture that gradually penetrates into the airtight case from the outside cannot be adsorbed over an extended period of time, so that ultimately the light emission characteristics of the organic EL element degrade.
The adverse effects of moisture gradually penetrating in from the outside are not limited to organic EL elements, but is a problem common to many types of electronic and optical equipment employing semi-hermetic enclosures as housings.
With the foregoing in view, it is an object of the present invention to provide an adsorbent molded article having sustained adsorption over an indefinite period; an adsorbent unit employing said adsorbent molded article; and a housing employing said adsorbent molded article or adsorbent unit.
This and other purposes of the present invention will become evident from review of the following specification.